This invention relates to ultrasonic imaging, or doppler and more particularly to an improved transducer structure useful in ultrasonic imaging or doppler, especially in the area of medical diagnosis.
Ultrasonic transducers are well known in the art and a large variety of shapes and sizes have been proposed. One particularly useful configuration for medical diagnosis is an annular array wherein one or more ring shaped transducing elements are arranged in concentric fashion about an axis in order to pulse energy into a body and to receive the reflected energy from internal organs. An example of such a transducer may be found in the Specht et al. U.S. Pat. No. 4,241,611, issued Dec. 30, 1980. This patent also notes that one of the rings may be dedicated to transmit energy while the remainder of the rings may be used to receive energy. Also, if the transmit ring is a separate ring, it can then be made of a different material which is more efficient as a transmitter than as a receiver. The Dorr et al. U.S. Pat. No. 3,327,286 issued June 30, 1967 also shows a sonic transducer having two annular elements one of which is a transmitter and the other of which is a receiver.
The difficulty with the prior art has been the problem of obtaining increased sensitivity without having beam pattern degradation. More specifically, it is desirable to have a beam pattern which is substantially symmetrical at all depths at which the transducer is to be used. I have determined that one way of obtaining this desired beam pattern is to construct a transducer array in which alternate ones of the transducer elements transmit radiation while the opposite alternate ones receive the reflected radiation and the area of all of the elements is substantially the same. Furthermore, by constructing a tranducer in this manner and utilizing a material for the transmitting elements which is chosen for high transmit sensitivity and utilizing a different material chosen for high receive sensitivity for the receiving elements an increase of sensitivity results.